堆積層上の粒子群の流動について

Abstract

Contrary to the most investigators' opinions that the deposit regime is uneconomical, some papers have reported this regime to be not necessarily uneconomic since the power requirement may decrease for velocities below the limit deposit velocity. Also, it is said that in all applications of industrial significance the system should be designed to prevent occurrence of this unsafe region because there is imminent danger of pipe blockage. Nevertheless, for the slurry pipeline system transporting coarse solid particles and involving difficulties in controling operational variables rigorously such as hydraulic dredging or hydraulic conveying of run-of-mine coal, it is inevitable for some or all of solids to deposit temporarily on the bottom of the pipe.On these bases there is an immediate need for relationships to use in estimating both the bed thicknesses and the hydraulic gradients under the flow conditions in the deposit regime.This paper presents results of investigations of design methods in this regime. Experiments were conducted to support the theoretical modeling effort for the particle size range 1.71-3.10 mm using a 25.9mm (ID) transparent plastic pipeline, with total length of approximately 10 m, mounted on the frame horizontally.The correlation of experimental data has shown that the ratio hr of the bed thickness to the pipe diameter D and the hydraulic gradient im of slurry flow may be determined from following equations if the functions of f1 (Cv) and f2 (Cv) are given experimentally:_??_in which: Va=apparent mean velocity of slurry flow; g=gravitational constant; Cv=delivered volumetric concentration of solids; v=kinematic viscosity of water; R, R0=hydraulic radii of the free flow section above the bed and of the pipe; Vt=terminal settling velocity of single particle;δ=specific gravity of solids.